The present invention relates generally to a reagent and method for the in vitro diagnosis of diseases, and more particularly, to coated polystyrene latex particles and their use in agglutination procedures for serological testing. This invention also relates to the diagnosis of the human autoimmune diseases, particularly the collagen or rheumatic diseases.
Upon infection by foreign matter of antigenic character, many animals exhibit an immunologic response. One aspect of this response is the presence in the animal's blood of antibodies, so-called circulating antibodies, capable of recognizing and binding the foreign material.
The animal's ability to distinguish its own organic matter from unwanted foreign material is obviously a preeminent feature of the immune response. Unfortunately, for reasons not completely understood, this fail-safe mechanism against self-reactivity sometimes breaks down, initiating a pathological state in the animal due to the presence of self-reactive, circulating antibodies. Indeed, the presence of self-reactive antibodies has been connected with an increasing number of diseases, such as hemolytic anemia, hyperthyroidism, thyroiditis, Sjorgren's syndrome, rheumatoid arthritis, polymyositis, scleroderma and systemic lupus erythematosus.
This latter group of five diseases, known as collagen or rheumatic diseases, has a number of common traits. Patients suffering from these diseases often exhibit circulating antibodies to a number of cell components. Of particular interest to clinicians are the antibodies directed against nuclear components, such as native deoxyribonucleic acid (native DNA), denatured deoxyribonucleic acid, deoxyribonucleoprotein, histones, Sm antigen, and ribonucleoprotein. These are believed to play a central role in the pathological condition.
A number of tests have been developed to detect circulating antibodies against nuclear materials. Perhaps the oldest of these tests is the LE cell preparation, a test exhibiting specificity for antideoxyribonucleoprotein. The LE cell preparation is positive with only about 70% of sera from active systemic lupus erythematosus patients, and is also positive in some sera of patients with drug-induced lupus syndromes, rheumatoid arthritis, other chronic connective tissue diseases, and chronic active hepatitis. Laboratory technicians basically consider the LE cell test tedious and generally unsuited for large scale screening.
For these reasons and others, the LE cell preparation has been replaced, to a large extent, by the indirect immunofluorescent anti-nuclear antibody (ANA) test, especially for routine testing purposes. The immunofluorescent ANA test can utilize a number of different substrates, because the components materials tested for, antinuclear antibodies, react with a variety of substrates. Four primary patterns of nuclear fluorescence, which apparently result from the presence of circulating antibodies directed against the various nuclear components, have been distinguished and must be recognized during testing. This complexity has introduced the need for technical expertise and expensive hardware to avoid making errors during the interpretation of test results.
Several other methods for the routine analysis of antibodies to individual nuclear components, including native DNA antibodies are also available. One DNA specific method incorporates the Farr ammonium sulfate globulin-precipitation technique and utilizes enzymes, fluorescence, or more commonly, radioactivity to label native DNA. To obtain reproduceable results, this procedure requires very careful attention to technique. A second DNA specific method is another immunofluorescent technique, which although utilizing the kinetoplast of the flagellate Crithidia lucillae as substrate, still shares many of the difficulties of the immunofluorescent ANA test. An additional procedure, the passive hemagglutination test, has also been developed, but its utility is somewhat curtailed due to the relative instability of the red blood cell carrier and the need for frequent recalibrations.
Much effort to improve the diagnostic process for detecting the rheumatic type of autoimmune disease has centered around the agglutination of latex particles. The practicality of latex reagents in diagnostic procedures has been known for a number of years, and by way of example, several latex procedures and reagents can be found in U.S. Pat. Nos. 3,088,875, 3,658,982, 3,826,613, 3,992,517, and German Pat. No. 1,914,081. Generally, a workable latex agglutination procedure should be reproducible, sensitive, suitable for large-scale screening, and relatively specific; and the latex particles should not autoagglutinate under routine storage conditions. A more effective latex reagent meeting these requirements is needed for in vitro diagnosis of autoimmune diseases, particularly systemic lupus erythematosus.